Electrical Load Calculator
Calculate total electrical load for circuits, panels, and service sizing
Electrical Service
NEC: 3 watts per sq ft for general lighting & receptacles
Major Appliances & Fixed Loads
Check all that apply and enter the wattage (nameplate rating)
Small Appliance & Laundry Circuits
Minimum 2 required by NEC (1,500 W each)
Minimum 1 required by NEC (1,500 W each)
Additional Custom Loads
Results
Step-by-Step Calculation (NEC Standard Method)
Understanding Electrical Load Calculations
An electrical load calculation determines the total power demand of a home or building. This is used to size the main service panel, service entrance conductors, and utility meter. The National Electrical Code (NEC) provides a standard method for calculating residential loads.
Key Formulas:
Watts = Volts × Amps
Amps = Watts ÷ Volts
Total Service Amps = Demand Load (watts) ÷ Service Voltage
NEC Standard Calculation Method (Article 220)
- General lighting load: 3 watts × total square footage of the home
- Small appliance circuits: 1,500 watts × number of circuits (minimum 2 for kitchen)
- Laundry circuit: 1,500 watts × number of circuits (minimum 1)
- Apply demand factor: First 3,000 watts at 100%, remainder at 35%
- Add fixed appliances: If 4 or more, apply 75% demand factor to the total
- Heating/cooling: Use the larger of heating or cooling load (they don't run simultaneously)
- Largest motor: Add 25% of the largest motor load
- Calculate amperage: Divide total demand watts by service voltage
Residential Service Panel Sizes
| Panel Size | Max Watts (240V) | Typical Home Size | Notes |
|---|---|---|---|
| 100 Amp | 24,000 W | <1,500 sq ft | Minimum for small homes, no electric heat or EV |
| 200 Amp | 48,000 W | 1,500-3,500 sq ft | Standard for modern homes, most common |
| 320 Amp | 76,800 W | 3,500-5,000 sq ft | Large homes with electric heat, EV charger, pool |
| 400 Amp | 96,000 W | >5,000 sq ft | Very large homes, workshops, multiple sub-panels |
Common Appliance Wattage Reference
| Appliance | Typical Watts | Voltage | Circuit |
|---|---|---|---|
| Electric Range/Oven | 8,000-12,000 | 240V | 40-50A dedicated |
| Electric Dryer | 4,000-5,500 | 240V | 30A dedicated |
| Water Heater | 3,500-5,500 | 240V | 30A dedicated |
| Central AC (3-ton) | 3,500-5,000 | 240V | 30-40A dedicated |
| Heat Pump | 4,000-7,000 | 240V | 30-50A dedicated |
| EV Charger (Level 2) | 3,800-11,500 | 240V | 30-60A dedicated |
| Dishwasher | 1,200-1,800 | 120V | 15-20A dedicated |
| Garbage Disposal | 500-1,500 | 120V | 15-20A |
| Microwave | 1,000-1,800 | 120V | 20A dedicated |
| Pool/Spa Pump | 1,500-3,000 | 240V | 20-30A dedicated |
Related Calculators
Important: This calculator provides estimates for planning purposes based on the NEC standard calculation method. Actual electrical load calculations for permits and installations must be performed by a licensed electrician and reviewed by your local building department. Electrical work should always be done by qualified professionals to ensure safety and code compliance.